The invention relates to a method of producing a composite component.
PCT International Publication No. WO 2008/125233 A1 discloses a method of producing a composite component in which a hollow section is expanded by internal high pressure and is simultaneously encapsulated with plastics material in a bulge region. The simultaneous expansion and encapsulation is intended to produce an improved positive lock.
With polymer hybrid components that are known per se, which are designed as a combination of an injection molded component and a hydroformed metal component, the composite adhesion between the two component parts of the component is brought about by an adhesion promoter or by a positive lock between the two components. The fixing of the two components relative to each other is, however, often inadequate despite these measures. Particularly in the case of hybrid components connected in positive manner, it is often not possible to produce a positive lock providing sufficient holding.
Exemplary embodiments of the present invention provide a method of producing a composite component that improves the composite adhesion in a composite component consisting of a hollow section which is expanded by internal high pressure and a plastics material portion.
With such a method, in a first step a region of a hollow section is expanded until it comes to lie against an edge region of a cavity of a combined hydroforming and injection mold. In a second step of the method, this still free cavity is filled with an injection molding compound. According to the invention, in a third step the hollow section, at least in regions, is expanded further, increasing the internal high pressure. Upon this expansion, a free form is produced, the shape of which depends on the pressure difference between the internal high pressure and the injection molding pressure, and also the temperature of the injection molding and the shear stresses triggered by the injected plastics material by flow contact on the surface of the hollow section. Due to the free form, particularly large undercuts are obtained, so that the molded on plastics material can clamp particularly well to the hollow section and thus achieves completely non-slip, non-detachable holding on the hollow section, and therefore the composite adhesion is considerably improved. Additional means providing holding, such as adhesives or other adhesion promoters and also mechanically acting fastening elements, can be dispensed with.
At the same time, owing to the temperature of the injection molding compound and the shear stresses acting on the hollow section during the third step due to the pasty or liquid injection molding compound, which result in an increase in the flow limit of the hollow section material, particularly high degrees of deformation can be achieved.
In a further embodiment of the invention, the injection molding compound is fed into the cavity preferably at a temperature of 200° C. to 400° C. The hollow section, which may advantageously be aluminum for the purpose of lightweight construction, likewise assumes this temperature. Since the material aluminum has a greater deformability in this temperature range, far higher degrees of deformation can be achieved when shaping these aluminum hollow sections. Advantageously, during the third step of the method in addition a specified pressure difference between the internal high pressure and a pressure of the injection molding compound is set, in order thus to control particularly well the shear stresses in the hollow section which is to be shaped and thus likewise to have a positive influence on the flow behavior of the material of the hollow section.
During the expansion of the hollow section in the third step of the method, furthermore preferably a valve, for example in the form of a needle valve, of at least one exit channel of the cavity is opened, so that injection molding compound displaced by the expansion of the hollow section can emerge from the cavity. This ensures that during the additional expansion in the third step of the method the excess injection molding compound does not result in uncontrolled over-encapsulation on the component.
Furthermore, the location and the number of the exit channels are likewise of relatively great significance for the shape or contour of the free form, so that when the valve is opened a particularly great surface change in the hollow section is produced, for example, in a wave form or peak form, which is precisely dependent on the number and form of the channels. In the case of a peak form, a positive lock on all sides is achieved, which also fixes the plastics material in rotation resistant manner on the hollow section.
In a further configuration of the invention, the expansion of the hollow section in the third step is ended if a specified residual volume of injection molding compound in the cavity is reached. This permits particularly simple monitoring of the progress of the method by measuring the volume of the plastics material emerging through the opened valve.
In a further embodiment of the invention, in a fourth step of the method the valve is closed and the internal high pressure of the hollow section is increased further. This means that additional calibration of the hybrid component and hence improvement of the material quality and the composite adhesion can be achieved.
The temperature of the injection mold is kept substantially constant during the entire expansion of the hollow section, in order to achieve as low as possible cooling of the injection molding compound, thus likewise to keep the temperature thereof constant and thus to maintain the desired effects on the flow limit of the material of the hollow section during the entire shaping process.
Preferably, when carrying out the method, a hollow section made from a deformable non-ferrous metal, preferably aluminum or an aluminum base alloy, is used. Precisely when using aluminum or aluminum base alloys, the aforementioned effects on the deformability due to temperature, shear stresses and back-pressure become particularly clearly noticeable, so that even with aluminum, which per se has low elastic limits, considerably greater degrees of deformation and hence a better positive lock between the hollow section and the plastics material portion can be achieved. Upon expanding the hollow section, in this case a maximum increase in diameter of 10% to 15% and in particular of 15% to 35% is achieved. This very considerably exceeds the degrees of deformation of 12% to 15% which are conventional for aluminum, so that even large undercuts between the metal and the plastics material portion can be achieved.